leetcode@ [97] Interleaving Strings

https://leetcode.com/problems/interleaving-string/

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 = "aabcc",
s2 = "dbbca",

When s3 = "aadbbcbcac", return true.
When s3 = "aadbbbaccc", return false.

class Solution {
public:
    bool isInterleave(string s1, string s2, string s3) {
        if(s1.length() + s2.length() != s3.length()) return false;
        if(s1.length() == 0 && s2.length() == 0 && s3.length() == 0) return true;
        
        vector<vector<bool> > dp(s1.length()+1, vector<bool>(s2.length()+1, false));
        for(int i=1;i<=s1.length();++i) {
            dp[i][0] = (s1.substr(0,i) == s3.substr(0,i))? true: false;
        }
        for(int j=1;j<=s2.length();++j) {
            dp[0][j] = (s2.substr(0,j) == s3.substr(0,j))? true: false;
        }
        
        for(int i=1;i<=s1.length();++i) {
            for(int j=1;j<=s2.length();++j) {
                if(dp[i-1][j] && s1[i-1] == s3[i+j-1]) dp[i][j] = true;
                else if(dp[i][j-1] && s2[j-1] == s3[i+j-1]) dp[i][j] = true;
                else dp[i][j] = false;
            }
        }
        
        return dp[s1.length()][s2.length()];
    }
};